It has long been assumed that early stereotyped behavior may function as a precursor to later self-injurious behavior in children with mental retardation and related developmental disabilities. Much of the speculation is focused on the possibility that some forms of early stereotyped behavior are shaped by successive approximation into self- injury through a process of differential reinforcement from primary caregivers. Face validity notwithstanding, this assumption has never been systematically studied. Consequently, it remains difficult to make statements with confidence about the early development of one of the most serious behavior problems afflicting children with mental retardation and related developmental disabilities. Our major goal is to begin systematic study of the correlates and progression of early aberrant stereotypies and self-injury. We assume that early identification of precursors and elucidation of behavioral mechanisms will lead to larger treatment studies designed to prevent or reduce the risk of later development of severe self-injury. In our preliminary work to date, we have identified a group of young children who are at high risk for developmental disability secondary to serious medical illness during infancy. Over half of our current sample (N=25) have some form of stereotyped or self-injurious behavior. The mean age of reported onset for stereotyped behavior was 26 months and for self-injury was 34 months. This suggests the possibility of a general sequencing with stereotypies preceding self-injury, however, the nature of this relation remains unclear. The children with stereotypies and self-injury had more large movements during infancy compared with the children without stereotypies and self-injury. Further study is needed to understand the nature of the relation between large motor movements during infancy and later stereotyped and/or self-injurious behavior. Our specific objective in this study is to prospectively follow a group of already identified medically fragile infants beginning at 18-months corrected age for a two- year period. infants will be directly observed at point of entry into the study and then quarterly for one-hour long sessions during structured and unstructured play conditions with primary caregivers. For each infant, prospectively collected data will be available on the amount of time hospitalized and the amount of technology required for their survival. These variables will be conceptualized as perinatal risk factors related to environmental restriction and examined in relation to infant large motor movements and subsequent stereotyped and self-injurious behavior. Two- way analysis of variance with repeated measures will be used to compare differences between infants grouped by the presence or absence of stereotypy and self-injury. Finally, child effects on caregiver interaction will be studied using lag sequential analysis and comparing sequential dependencies between caregiver responsivity over time to infants with and without stereotypy and self-injury.